It is known to provide at least one layer of a stretched monofilament as a reinforcement for a core tube of thermoplastic material and to constitute that layer as a coil or helix. The core tube can be extruded at the same time as the coil reinforcement is applied thereto or extruded beforehand and can have the coil wound therearound. The core tube which is provided with the coil reinforcement can be constituted so that it is practically rigid or flexible and hoselike, as desired. The term "tube"as used herein, therefore, should be understood to include both relatively rigid pipe structures as well as highly flexible hose structures and the entire range of rigidity between these two extremes.
The core tube itself can be formed as a single layer or as a multilayer composite and can, for example, have an inner layer forming a protective layer or film to prevent an attack by the fluid conducted through the tube. The outer layer can, for example, also be determined by the environment in which the tube is to be used, for example, by the mechanical properties which the tube must have to withstand, environmental factors, or the thermal requirements of the tube, for example, its resistance to hot or cold environments.
In the past, tubes of this type have been made utilizing prefabricated synthetic resin monofilaments as the reinforcing coil strand.
The core tube, whether previously made or extruded at the time, is passed through a coiling machine which generally has one or more spools of the prefabricated monofilament disposed around the periphery of the core tube and located therearound so that each prefabricated monofilament would be helically wound around the core tube.
This process is expensive and highly unreliable or subject to breakdown.
For example, the bobbins or spools must be provided with an endless length of the monofilaments to be effective. In practice, the monofilament is fabricated elsewhere and may be interrupted on the spool. Because the winding of the monofilament on the spool may be irregular, the prefabricated monofilament may break from time to time as it is drawn off the spool.
When such breakage occurs, again the length of monofilament is interrupted on the spool and the system may have to be shutdown to enable restoration of the continuity of the reinforcing filament that is to be wound around the core tube.
Also, the system is subject to costly standstill as the spools empty and must be replaced by new spools.
Furthermore, the means required to generate different degrees of stretch of the preformed monofilament or monofilaments used as reinforcing strands are expensive and complex and prone to breakdown and are not readily controllable during production runs.
Accordingly, prior art reinforcing methods and the resulting products have left much to be desired